The Dow Corning Corporation has submitted the summarized preliminary results from a 28-day inhalation study of trimethoxysilane (CAS No. 2487-90-3) in male and female rats. Exposures to the chemical at chamber concentrations of 0.5, 5.0, and 10.0 parts per million were reportedly carried out for five (5) days per week, seven (7) hours per day for four (4) weeks. At the highest dose, 60% of the animals had died after 2-3 weeks of exposure. High dose exposure was terminated by the 21st day and the remaining rats sacrificed in order to provide clinical and pathological data. At the mid-dose, 40% of the animals had died by the end of the fourth week. Neither the control (air) group nor the low-dose group experienced any mortality in the experiment. The submitter reports that significant decreases in both food consumption and body weight and general weakness with moderate to severe lung congestion were observed in the high and mid-dose animals of both sexes. Significant deviations from control values were also found in hematological parameters (males and females; mid and high dose) and blood biochemical parameters (females; high dose). Subacute to chronic bronchitis and bronchiolitis were observed in all rats (male and female) exposed to trimethoxysilane at 5 and 10 ppm; similar lesions were reportedly not found in the 0.5 ppm dose group or in the control group.